This invention relates to traveling wave tubes of the folded waveguide type for use at very high frequencies, frequencies in the 100 GHz band where the dimensions of the waveguide are so small that special machining techniques are required to provide a structure which will have electrical characteristics which are required to allow the traveling wave tube to function properly. Prior to this invention, the folded waveguide interaction circuit of the traveling wave tube and the input/output transitions to standard waveguide, type WR-10 for the 100 GHz range, were made of separate pieces. The fabrication of traveling wave tubes from these component parts by aligning the parts and subsequently brazing the parts to provide an integral unit was particularly difficult to do in the 94 GHz band where the internal circuit folded waveguide cross-section is only 0.010 inches by 0.07 inches. Any misalignment, even of 0.001 inches, causes severe VSWR reflection at the junction between the folded waveguide circuit and the input/output transitions. In actual construction of a 44 GHz folded waveguide traveling wave tube, a minor misalignment at the folded waveguide circuit-to-transition braze resulted in a VSWR of nearly 3 to 1. For the traveling wave tube intended for operation at 44 GHz, the internal circuit folded waveguide dimensions are 0.025 inches by 0.144 inches. Obviously, the problem of alignment and brazing of the folded waveguide circuit and the transition is much more severe for traveling wave tubes intended to operate at 94 GHz.